The present invention relates to a waste heat recovering device for a multi-cylinder internal combustion engine.
Known as waste heat recovering devices of this type are a device including a heat exchanger in each of a plurality of exhaust pipes extending from cylinders of a multi-cylinder internal combustion engine (see Japanese Patent Application Laid-open No. 56-156407, for example) and a device including a heat exchanger in a collecting pipe which is collection of a plurality of exhaust pipes extending from cylinders of a multi-cylinder internal combustion engine (see Japanese Patent Application Laid-open No. 5-340241, for example).
However, the former needs as many heat exchangers as the cylinders, and thus has a problem that, for example, after operation of a heat exchanger in the first cylinder in firing order, further operation thereof cannot be performed until just before an end of an exhaust process of the last cylinder in the firing order, causing a long rest period of each heat exchanger, and each heat exchanger is thus cooled during the period to reduce heat recovery efficiency. Further, if the former is for vehicle use, it has problems that an evaporator is provided in each cylinder to increase a size of an engine itself, for example, by increasing an interval between adjacent cylinders for the evaporator to be mounted, and that the evaporator occupies a large space in an engine compartment to result in an impediment to securing spaces for other components to be located.
On the other hand, the latter has a problem that when a collecting portion is formed at a long distance from an exhaust port in order to avoid exhaust interference, and an evaporator is provided in the collecting portion, temperature of exhaust gas decreases to reduce heat recovery efficiency by the evaporator. On the contrary, when the collecting portion is provided at a short distance from the exhaust port without considering the exhaust interference in order to utilize high-temperature exhaust gas, the exhaust interference reduces output of the internal combustion engine and thus exhaust pulses, thereby reducing the heat recovery efficiency by the evaporator.
The present invention has an object to provide a waste heat recovering device for a multi-cylinder internal combustion engine in which output of a multi-cylinder internal combustion engine is rarely reduced, and the number of heat exchangers is reduced compared to the number of cylinders of the engine to reduce rest periods of the heat exchanger and reduce spaces occupied by the heat exchanger.
To attain the above described object, the present invention provides a waste heat recovering device for a multi-cylinder internal combustion engine including one or more collecting pipes that are collection of a plurality of exhaust pipes unlikely to cause exhaust interference, among a plurality of exhaust pipes extending from cylinders of a multi-cylinder internal combustion engine, a heat exchanger for recovering heat of exhaust gas being provided in the one or more collecting pipes.
When exhaust pipes extending from a plurality of cylinders whose exhaust periods partially overlap are collected with their lengths reduced, exhaust interference occurs to reduce output of a multi-cylinder internal combustion engine. However, even when exhaust pipes extending from a plurality of cylinders whose exhaust periods do not overlap are collected with their lengths reduced, exhaust interference is unlikely to occur, thus rarely reducing the output of the multi-cylinder internal combustion engine.
Configured as described above in this view, the output of the multi-cylinder internal combustion engine is rarely reduced even when the exhaust pipes are collected with their lengths reduced. Further, the number of the heat exchangers is smaller than the number of the cylinders, thus rest periods of the heat exchangers can be reduced.
Reduction in the length of the exhaust pipe as described above allows the exhaust gas to be introduced in the heat exchanger with its temperature reduction minimized, and also the rest period of the heat exchanger is reduced, thereby allowing increase in heat recovery efficiency of the exhaust gas. Further, attendant on the reduction of the heat exchangers, spaces occupied by them can be reduced to achieve reduction in size and cost of the device, which is suitable for vehicle use.